Automatic balancing device

ABSTRACT

Provided herein is an automatic balancing device for counterbalancing an out-of-balance mass present in a rotating body. The automatic balancing device includes a chamber with an outer wall and an axis, first and second counterbalancing masses constrained to move freely in a circular path about the axis within the chamber, and a viscous fluid provided in the chamber so as to provide viscous coupling between the outer wall of the chamber and each of the counterbalancing masses. The counterbalancing masses may be arranged so that the first counterbalancing mass leads the second counterbalancing mass when the device is in use. A constraint may be provided with the device so as to prevent the first counterbalancing mass from leading the second counterbalancing mass by more than substantially 180°.

FIELD OF THE INVENTION

The invention relates to an automatic balancing device forcounterbalancing an out-of-balance mass present in a rotating body.Particularly, but not exclusively, the invention relates to an automaticbalancing device for use in washing machines and for counterbalancingout-of-balance masses present in the washing machine during washing andspinning cycles.

BACKGROUND OF THE INVENTION

Automatic balancing devices for counterbalancing out-of-balance massesare known in many different applications. However, the most complexout-of-balance situations occur when both the position and size of theout-of-balance mass is unpredictable and the speed of rotation isvariable, as in the case of a washing machine. Many different automaticbalancing devices have been proposed and used in washing machines andmany of these are effective at counterbalancing out-of-balance masses atspeeds above the critical speed (ie. the speed of resonance of thesystem). Examples of this type of automatic balancing device are shownin GB1,035,033; GB1,092,188; WO 93/23687; WO 95/32372; U.S. Pat. Nos.5,813,253; 5,862,553; DE1 912 481. All of the devices shown in thesedocuments make use of the phenomenon by means of which, at speeds ofrotation above the critical speed, freely rotatable counterbalancingmasses automatically take up positions in which the out-of-balance massis counterbalanced. However, it is recognised in some of theaforementioned documents that, at speeds below the critical speed,freely rotating counterbalancing masses act so as to exacerbate theexcursion of the rotating body due to the presence of the out-of-balancemass. In these cases, the counterbalancing masses are proposed to belocked in a fixed position with respect to the chamber in which they arelocated when the body is rotating at a speed below the critical speed.In the case of U.S. Pat. No. 5,813,253, a roller locates in a recess inorder to prevent the balancing masses from moving along the annular pathin which they run. The roller is released from the recess when the bodyexceeds the critical speed. In GB1,092,188, the counterbalancing massesare pivotably mounted about an axle with locking members provided tolock the masses in a fixed position with respect to the chamber in whichthey are housed when the speed of rotation is below critical. Thelocking means release when the speed is above critical. It is alsoenvisaged in this prior art document that the counterbalancing memberscould be locked together, so that they have a zero net out-of-balanceeffect until the critical speed has been exceeded.

The known mechanisms by means of which counterbalancing masses can belocked in a position in which they have a zero net out-of-balance effectare generally difficult and expensive to manufacture. They aresusceptible to damage in view of the movement of the counterbalancingmasses, which can sometimes be quite violent. However, in arrangementswhich do not lock the counterbalancing masses, acceleration of the drumof the washing machine from a below-critical speed to an above-criticalspeed can cause extreme excursion, especially at the critical speed.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an automatic balancingdevice for counterbalancing an out-of-balance mass present in a rotatingbody in which, during acceleration through the critical speed, theamount of excursion of the rotating body is minimised. It is a furtherobject of the present invention to provide an automatic balancing devicewhich is economic to manufacture and less susceptible to damage thanknown arrangements. It is a further object of the present invention toprovide a method of operating a washing machine in which rotation of thedrum can be accelerated through the critical speed with the minimum ofexcursion.

The invention provides an automatic balancing device forcounterbalancing an out-of-balance mass present in a rotating body, theautomatic balancing device comprising a chamber having an outer wall andan axis, first and second counterbalancing masses constrained to movefreely in a circular path about the axis and within the chamber, and aviscous fluid provided in the chamber so as to provide viscous couplingbetween the outer wall of the chamber and each of the counterbalancingmasses when the device is in use, characterised in that thecounterbalancing masses are adapted and/or arranged such that, in use,the first counterbalancing mass leads the second counterbalancing mass,and constraining means are provided so as to prevent the firstcounterbalancing mass from leading the second counterbalancing mass bymore than substantially 180° when the device is in use.

Preferably, the first counterbalancing mass has a moment of inertiawhich is lower than that of the second counterbalancing mass. Morepreferably, the viscous coupling between the first counterbalancing massand the outer wall of the chamber is higher than the viscous couplingbetween the second counterbalancing mass and the outer wall of thechamber.

The arrangement on this invention has been found to be effective inreducing the amount of excursion of the rotating body in comparison toan arrangement utilising no counterbalancing means, at least when usedin a washing machine. Indeed, the claimed arrangement is capable ofreducing the maximum excursion of the rotating drum of a washing machineto a level significantly below that currently achieved by commerciallyavailable washing machines which utilise a known balancing device. Thereduction in excursion is particularly important as the rotating bodypasses through the critical speed as the excursion is largest at thisspeed. Reducing the excursion, particularly at the critical speed,allows washing machines and other similar devices to be manufacturedwith larger drums because less provision for excursion needs to be made.Also, less ballast needs to be provided.

The arrangement of this invention is also very simple to manufacture andreliable in operation. In place of the known locking arrangementsdescribed in the prior art discussed above, the constraining means cantake a very simple form which results in higher reliability and lowerfailure rates than more complex arrangements. The manufacturing cost ofthe claimed arrangement is also lower than the cost of the known priorart arrangements.

The arrangement of this invention is believed to operate in thefollowing manner. When the rotating body is rotated at a speed belowcritical but sufficient to cause the counterbalancing masses to rotatewithin the chamber, the counterbalancing masses spread apart because thefirst counterbalancing mass leads the second counterbalancing mass. Asthe speed of the device increases, the spread of the masses willincrease until, when the spread is at or near 180°, they are preventedfrom spreading apart any further by the constraining means. In thisposition, i.e., when the masses are spread apart by approximately 180°,they contribute little or nothing to the out-of-balance mass present inthe rotating body and the excursion of the rotating body is notexacerbated. However, at the same time, the excursion of the rotatingbody causes the masses to be drawn towards one another. Because themasses are free to move with respect to the chamber (within theconstraints applied by the constraining means), they move towards oneanother thereby effecting a partial balancing of the out-of-balance massin the rotating body. This movement of the masses affects the phase andsize of the excursion of the rotating body which then causes furthermovement of the masses in response. Hence the masses are in constantmovement with respect to the chamber, continually moving into a positionin which the out-of-balance mass is partially balanced. This results ina reduction of the excursion of the rotating body.

It is also believed that, as the speed of rotation of the rotating bodyapproaches resonance (the critical speed), the counterbalancing massestend towards a position in which the out-of-balance mass is fullybalanced. Thus the amount by which the excursion of the rotating body isreduced increases as the rotating body approaches resonance.

The invention also provides a method of operating a washing machinehaving a drum and incorporating the automatic balancing device describedabove, the method comprising the steps of:

-   (a) rotating the drum and the automatic balancing device at a speed    below the critical speed of the washing machine whilst allowing each    of the counterbalancing masses to rotate freely about the axis;-   (b) causing the first counterbalancing mass to lead the second and    any further counterbalancing mass;-   (c) preventing the first counterbalancing mass from leading the    second and any further counterbalancing mass by more than    substantially 180°; and-   (d) increasing the speed of rotation of the drum to a speed above    the critical speed of the washing machine.-   Preferably, the method comprises the further steps of:-   (e) detecting variations in the amplitude of excursion of the drum    due to the presence of an out-of-balance load therein and the    counterbalancing masses;-   (f) detecting a minimum amplitude of excursion; and-   (g) commencing the increase in the speed of rotation of the drum to    a speed above the critical speed of the washing machine at a time    when the amplitude of excursion is at or close to a minimum.

Preferably, the speed of rotation of the drum is increased from a speedbelow the critical speed of the washing machine to a speed above thecritical speed of the washing machine at a rate of between 5 rpm/s and50 rpm/s, more preferably between 5 rpm/s and 15 rpm/s.

It is believed that the rate of acceleration of the drum can have aneffect on the amount by which the excursion of the rotating body isreduced. Slower rates of acceleration have been shown to improve theeffect. It is believed that this is due to the fact that slower rates ofacceleration allow the counterbalancing masses time to adopt new,advantageous positions which will minimize the excursion experienced asthe rotating body passes through resonance.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic sectional side view of a washing machineincorporating an automatic balancing device according to a firstembodiment of the invention;

FIG. 2 is a sectional side view through the automatic balancing deviceshown in FIG. 1;

FIG. 3 a is a plan view of one of the counterbalancing masses formingpart of the automatic balancing device shown in FIG. 2;

FIG. 3 b is a perspective view of the counterbalancing mass of FIG. 3 afrom the opposite side;

FIG. 4 a illustrates the interaction of two counterbalancing masses ofthe type shown in FIGS. 3 a and 3 b in use in the automatic balancingdevice of FIG. 2 in a first position;

FIG. 4 b illustrates the interaction of the same two counterbalancingmasses in a second position;

FIG. 5 is a schematic front view of an automatic balancing deviceaccording to a second embodiment of the invention;

FIG. 6 is a perspective view of a collar forming part of the device ofFIG. 5;

FIG. 7 illustrates the position and operation of the collar of FIG. 6with respect to two counterbalancing masses forming part of the deviceshown in FIG. 5;

FIG. 8 a illustrates the positioning of the masses of FIG. 5 inside achamber;

FIG. 8 b shows the surface of one of the masses of FIG. 5;

FIG. 9 illustrates a third embodiment of the invention; and

FIGS. 10 a, 10 b and 10 c illustrate alternative counterbalancing massessuitable for use in the embodiments illustrated in FIGS. 1 to 9.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a typical environment in which an automatic balancingdevice is useful and desirable. FIG. 1 shows a washing machine 10 havingan outer casing 12 and a tub 14 mounted inside the outer casing 12 byway of a system of springs and dampers 15. A perforated drum 16 ismounted inside the tub 14 so as to be rotatable about an axis 18. Inthis embodiment, the axis 18 extends horizontally although this is notessential. A hinged door 20 is located in the front face of the outercasing 12 in such a manner that, when the door 20 is in a closedposition (as illustrated), the tub 14 is sealed in a watertight manner.The door 20 is openable to allow articles of laundry to be placed insidethe drum 16 prior to the commencement of a washing cycle to be carriedout by the washing machine 10. Flexible seals 22 are also providedbetween the drum 16 and the door 20 so that moderate movements of thedrum 16 with respect to the outer casing 12 can be tolerated.

The drum 16 is mounted in a rotatable manner by way of a shaft 24 whichis supported in cantilever fashion in the washing machine 10 and drivenby a motor 26. The shaft 24 passes through the tub 14 and into theinterior thereof so as to support the drum 16. The drum 16 is fixedlyconnected to the shaft 24 so as to rotate therewith about the axis 18.It will be understood that the shaft 24 passes through the wall of thetub 14 in such a manner as to cause no rotation of the tub 14. Suchmounting arrangements are well known in the art. The washing machine 10also includes a soap tray 28 for the introduction of detergent, one ormore water inlet pipes 30 leading to the tub 14 via the soap tray 28,and a water drain 32 communicating with the lower-portion of the tub 14.

All of the features thus far described in relation to the washingmachine 10 are known per se and do not form essential parts of thepresent invention. Common variants of any or all of these features maytherefore be included in a washing machine capable of incorporating orutilising an automatic balancing device according to the invention ifdesired.

The present invention relates to an automatic balancing device suitablefor use in a washing machine of the general type described above. In theembodiment shown, the automatic balancing device 50 is located on thedistal end of the shaft 24, inside the drum 16 and adjacent the rearwall 16 a thereof. However, an automatic balancing device 50 of the typedescribed below can also be located on the outside of the drum 16, stilladjacent the rear wall 16 a thereof, but on the side facing the tub 14.It is also possible to provide the automatic balancing device at otherpositions along the shaft 24; for example, between the tub 14 and theouter casing 12, although such an arrangement is not the preferredposition.

The automatic balancing device 50 is illustrated in a rest position inFIG. 2. The automatic balancing device 50 has a cup-shaped cover 52which, together with a circular plate 53 lying next to the rear wall 16a of the drum 16, forms an outer wall 54 defining a chamber 56. Thecover 52 is fixedly attached to the circular plate 53 so that thechamber 56 is liquid-tight for reasons which will be explained below.The means of connection between the cover 52 and the circular plate 53are not material to the invention. The circular plate 53 can be attachedto the rear wall 16 a of the drum 16 if desired. The cover 52 is fixedlyattached to the distal end 24 a of the shaft 24 and is rotatabletherewith so that, when the shaft 24 is rotated by the motor 26 aboutthe axis 18, the cover 52 is rotated as well. The shaft 24 passesthrough the chamber 56 from the circular plate 53 to the cover 52.

Two counterbalancing masses 80 a, 80 b are rotatably mounted on theshaft 24. The masses 80 a, 80 b are mounted on the shaft 24 via bearings58 so that the masses 80 a, 80 b are able to rotate freely about theshaft. Means (not shown) are provided on the shaft 24 for preventing themasses 80 a, 80 b from moving axially along the shaft 24, theirpositions being maintained with respect to one another and with respectto the cover 52. The chamber 56 contains a pool of oil 60 (or otherviscous liquid) which is sufficiently deep to ensure that thecounterbalancing masses 80 a, 80 b are partially submerged as shown inFIG. 2. Indeed, it is preferred that there is sufficient oil 60 in thechamber 56 to ensure that, when the automatic balancing device 50 isrotated at a speed sufficient to distribute the oil 60 about theperiphery of the chamber 56, the counterbalancing masses 80 a, 80 b arestill partially submerged in, or at least in contact with, the oil 60.

The counterbalancing masses 80 a, 80 b are identical to one another. Theconfiguration of one of the masses 80 a is shown in detail in FIGS. 3 aand 3 b. Essentially, the mass 80 a comprises a disc portion 82 a whichis relatively slim in depth and circular in plan view. A mass portion 84a is provided on the disc portion 82 a and is rigidly fixed thereto.Indeed, the mass portion 84 a can be formed integrally with the discportion 82 a if desired. In the embodiment shown, the mass portion 84 aoverlies an area of the disc portion 82 a amounting to approximately onequarter, but the extent of overlie is not important. What is importantis that the shape of the mass portion allows the centre of gravity ofthe mass 80 a to be located a significant distance from the centre ofthe disc portion 82 a. A central aperture 86 a is located in thegeometric centre of the disc portion 82 a and passes through both thedisc portion 82 a and the mass portion 84 a. The aperture 86 a isdimensioned so as to receive the bearings 58 by means of which the mass80 a is mounted on the shaft 24. The function of the mass portion 84 ais to provide the counterbalancing mass 80 a with an eccentric centre ofgravity and sufficient mass to allow the mass 80 a to function as acounterbalance to an out-of-balance load present in the drum 16 of thewashing machine 10 during its operation.

The mass portion 84 a is delimited by an edge or lip 88 a. The edge orlip 88 a comprises a surface which extends generally perpendicular tothe circular faces of the disc portion 82 a. The edge or lip 88 aincludes two abutment surfaces 90 a, 92 a whose function will bedescribed below.

The mass 80 a carries a pin 94 a which protrudes beyond the surface ofthe disc portion 82 a but does not protrude beyond the surface of themass portion 84 a. The pin 94 a extends beyond the surface of the discportion 82 a, and perpendicular thereto, by an amount which is greaterthan the smallest distance a between the counterbalancing masses 80 a,80 b as shown in FIG. 2. However, the distance protruded by the pin 94 ais not as great as the larger distance A between the two masses 80 a, 80b, as will be explained below.

The counterbalancing mass 80 b is identical to the counterbalancing mass80 a described above. Parts of the counterbalancing mass 80 b will nowbe referred to using the reference numeral assigned to the correspondingpart of mass 80 a, but with the letter “a” replaced by the letter “b”.

The arrangement of the counterbalancing masses 80 a, 80 b in theautomatic balancing device 50 is shown in FIG. 2. The firstcounterbalancing mass 80 a is positioned to the left as shown and thesecond counterbalancing mass 80 b is positioned to the right. As hasbeen mentioned, the distance a between the masses 80 a, 80 b in the areawhere the mass portions 84 a, 84 b overlap is less than the distance bywhich the pin 94 b protrudes beyond the disc portion 82 b of the mass 80b. However, the distance A between the disc portions 82 a, 82 b isgreater than the extent of protrusion of the pin 94 b from the discportion 82 b. Thus the distal end of the pin 92 b is constrained totravel between the abutment surfaces 90 a, 92 a passing across the discportion 82 a and not across the mass portion 84 a. At each end of thepossible travel path of the pin 94 b relative to the mass 80 a, the pin94 b will contact one of the two abutment surfaces 90 a, 92 a of theother mass 80 a.

The rest position of the two masses 80 a, 80 b is shown in FIG. 4 a. Thefact that the masses 80 a, 80 b are identical means that, in the absenceof the pin 94 b, the masses 80 a, 80 b would lie alongside one anotherin alignment. However, because the pin 94 b may not lie alongside themass portion 84 a of the mass 80 a, it abuts against the abutmentsurface 90 a of the mass 80 a. Hence the masses 80 a, 80 b lie slightlyout of alignment in the rest position as shown in FIG. 4 a. It will beappreciated that, in the arrangement shown in FIG. 2, the pin 92 a ofthe mass 80 a is in fact redundant.

In operation, the automatic balancing device 50 operates as follows.Rotation of the drum 16 is effected by rotation of the shaft 24. Theautomatic balancing device 50 rotates with the shaft 24 and the drum 16so that the whole of the outer wall 54 of the chamber 56 rotates at arelatively high speed. By this we mean that the speed of rotation of thedrum 16, and thus the chamber 56, is sufficient to create centrifugalforces which will overcome gravitational forces and so maintain the loadcontained within the drum pressed against the wall thereof but is belowthe critical speed of the washing machine. Hence the counterbalancingmasses 80 a, 80 b are not in a position to perform an automaticcounterbalancing function. However, the viscous coupling provided by theoil 60 between the outer wall 54 of the chamber 56 and thecounterbalancing masses 80 a, 80 b will cause the counterbalancingmasses 80 a, 80 b to rotate about the shaft 24. Due to the dynamics ofthe system, the masses 80 a, 80 b will rotate about the shaft 24 at arotational speed which is lower than that of the shaft 24 and the drum16. Because of the shaping of the masses 80 a, 80 b, and particularlythe fact that a significant proportion of the surface of the mass 80 bfacing the circular plate 53 is spaced further from the circular plate53 than the whole of the surface of the mass 80 a facing the cover 52,the viscous coupling between the outer wall 54 and the mass 80 a will behigher than the viscous coupling between the outer wall 54 and the mass80 b. Hence, the mass 80 a will rotate at a speed closer to that of thedrum 16 and the chamber 56 than the mass 80 b. The result of this isthat the mass 80 a will become the leading mass and that the mass 80 bwill trail behind it. Moreover, the mass 80 a will rotate about theshaft 24 at a higher angular velocity than the mass 80 b. Furthermore,the abutment of the pin 94 b against the abutment surface 90 a willeliminate any possibility of the mass 80 a from lagging behind the mass80 b. In the embodiment shown, the location of the pin 94 b and theabutment surface 90 a will in fact ensure that the mass 80 a alwaysleads the mass 80 b.

As the drum 16 and chamber 56 rotate about the shaft 24 in the directionshown by the arrow B in FIG. 4 b, the trailing mass 80 b will trailfurther behind the leading mass 80 a. The masses 80 a, 80 b thus spreadapart with the mass 80 a leading and the mass 80 b trailing behind it byan increasing amount. However, as the angle by which the mass 80 btrails the mass 80 a approaches 180° (see FIG. 4 b), the pin 94 b abutsagainst the abutment surface 90 a thus preventing the mass 80 b fromlagging behind the mass 80 a by more than 180°. In the embodiment shown,the mass 80 b is constrained to lag the mass 80 b by less than 180°.Even so, the combined effect of the counterbalancing masses 80 a, 80 bon the rotating body in this position is small.

It has been found that, by allowing the counterbalancing masses 80 a, 80b to rotate freely within the constraints described above, the maximumamount of excursion of the drum 16 can be kept to a minimum as the drum16 is accelerated from the speed described above, through the criticalspeed to a spin speed high enough to extract water from the load carriedin the drum 16. Spin speeds are commonly 1400 to 1600 rpm at present. Itis advantageous if the rate of acceleration of the drum 16 is kept to amoderate rate: a rate of increase of speed of between 5 and 50 rpm persecond is generally regarded as favorable, with a rate of increase of 5to 15 rpm/s being more favorable still. Hence, in operation, the speedof the drum 16 is increased at a rate of between 5 and 50 rpm/s(preferably between 5 and 15 rpm/s) from the relatively high speedmentioned above to a suitable spin speed (typically 1400 to 1600 rpm)without constraining or otherwise locking the counterbalancing masses 80a, 80 b to one another or to the outer wall 54 of the chamber 56. Inthis way, the excursion of the drum 16 at the critical speed is reducedin comparison to other systems. This allows the dimensions of the drum16 to be maximized for any given size of washing machine and/or the riskof damage occurring when large loads are spun at high speeds to beminimized. Above the critical speed, the masses 80 a, 80 b automaticallyadopt positions which will counterbalance any out-of-balance present inthe drum 16, as is well known.

Optionally, a sensing device 27 (shown in dotted lines in FIG. 1) may beconnected to the motor 26. The sensing device 27 detects the currentdrawn by the motor 26 and/or the running speed of the motor 26. As themasses 80 a, 80 b adopt different relative positions, and thus perform agreater or lesser counterbalancing effect over time, either a minimumcurrent drawn by the motor 26 or a maximum speed of rotation of themotor 26 will be indicative of a position of greatest counterbalancingeffect. At these positions, the excursion of the drum 16 will be at aminimum for a given speed. It is believed to be beneficial to detectwhen these periods of minimum excursion occur and to initiate theacceleration of the drum 16 to the required spin speed at a point intime when the excursion is at or close to a minimum. Experimentalresults have shown that initiating the acceleration at such a time isadvantageous in many cases.

In a method of operating the washing machine of FIG. 1, when it isdesired to rotate the drum at speeds high enough to extract wash liquoror rinse water by spinning, the drum is first rotated at a speed whichis sufficient to stick the washload to the walls of the drum but belowthe critical speed. The masses 80 a, 80 b are allowed to rotate freelyabout the shaft 24, although the engagement of the pin 94 b againstabutment surfaces 90 a, 92 a prevents the mass 80 b from leading themass 80 a at all or from lagging the mass 80 a by more than 180°. Thedifference in the viscous coupling between the outer wall 54 of thechamber 56 and each of the masses 80 a, 80 b causes the masses initiallyto spread apart. Thereafter, the masses 80 a, 80 b will redistributethemselves under the influence of various forces and will, periodically,take up positions which cause maxima and minima of excursion of the drum16 and the shaft 24. If the motor 26 has coupled to it a sensing device27 as described above, the speed of and/or current drawn by the motor 26is monitored and a minimum value of either characteristic is sensed. Thedrum 16 is then accelerated to the desired spin speed. This willinevitably require the speed of rotation of the drum to pass through thecritical speed, at which the excursion of the drum 16 is greatest. Therate of acceleration is between 5 and 15 rpm/s but could be as high as50 rpm/s. By allowing the masses 80 a, 80 b freedom to rotate about theshaft 24 during the acceleration step, the maximum excursion is kept aslow as possible. Also, by initiating the acceleration of the drum 16from the lower speed at a point when the excursion is at or close to aminimum (as sensed by the sensor 27), the excursion experienced by thedrum 16 at the critical speed is minimized. Above the critical speed,the masses 80 a, 80 b position themselves, as is well known, so as tocounterbalance the out-of-balance load within the drum 16 and so theexcursion of the drum 16 at speeds above critical is greatly reducedand, in some cases, eliminated.

Keeping the maximum excursion of the drum 16 to a minimum is beneficialbecause a lower provision for excursion then needs be built into themachine and thus the size of the drum 16 can be increased in comparisonto other machines. Also, the risk of damage occurring due to excessiveexcursion of the drum 16 is reduced.

A second embodiment of the invention is illustrated in FIGS. 5, 6 and 7.FIG. 5 is a cutaway front view of an automatic balancing device 150having an outer wall 154 delimiting a cylindrical chamber 156. A shaft124, which is rotatable about an axis 118, passes through the chamber156. Two counterbalancing masses 180 a, 180 b are mounted on the shaft124 via bearings 158 so as to be freely rotatable about the shaft 124.The counterbalancing masses 180 a, 180 b are shaped so as to increase inbreadth with distance from the shaft 124. As with the masses 80 a, 80 billustrated in FIGS. 2, 3 and 4, the effect of this is to space thecentre of gravity of each counterbalancing mass 180 a, 180 b away fromthe axis 118.

Located between the counterbalancing masses 180 a, 180 b is a collar 190which is shaped and dimensioned to be supported on and freely rotatableabout the shaft 124.

Projecting outwardly from a first annular face 192 a of the collar 190are two diametrically opposed pins 194 a. A single pin 194 b projectsoutwardly from a second annular face 192 b of the collar 190, the pin194 b being aligned with one of the pins 194 a. The pins 194 a, 194 bproject sufficiently far from the respective annular surfaces 192 a,192b to engage with the counterbalancing masses 180 a, 180 b as they rotateabout the shaft 124.

The dimensions of the collar 190 and the positioning of the pins 194 a,194 b thereon are such that the pins 194 a abut against the edges of thecounterbalancing mass 180 a with little or no play as shown in FIG. 5.Thus the collar is held in a substantially fixed position with respectto the counterbalancing mass 180 a. However, since the counterbalancingmass 180 b is acted upon by only the single pin 194 b, it is able tomove relative to the counterbalancing mass 180 a between a firstposition in which the masses 180 a, 180 b are aligned and a secondposition in which the masses 180 a, 180 b are diametrically opposed. Thepositioning of the pin 194 b is such that the mass 180 a is not allowedto lag behind the mass 180 b. As in the previous embodiment, the viscouscoupling between the outer wall 154 and the mass 180 a is higher thanthat between the outer wall 154 and the mass 180 b. This can be achievedin any suitable way.

One way to vary the viscous coupling between the outer wall 154 and therespective masses 180 a, 180 b is illustrated in FIG. 8 a. Here, themass 180 a is arranged so as to be closer to the outer wall 154 than themass 180 b. An alternative way of ensuring that the viscous couplingbetween the outer wall 154 and the mass 180 a is higher than thatbetween the outer wall 154 and the mass 180 b is to provide the surfaceof the mass 180 a with an uneven or textured finish, as illustrated inFIG. 8 b. This non-planar finish need only be applied to the part of thesurface of the mass 180 a facing the outer wall, if desired, althoughmore of the surface can be finished in this way. Further alternativemeans for ensuring that the viscous coupling between the outer wall 154and the mass 180 a is higher than that between the outer wall 154 andthe mass 180 b will be apparent to a skilled reader.

In the embodiments described above, only two counterbalancing masseshave been provided. It is possible to provide more than two masses andan arrangement showing the use of three masses is shown in FIG. 9. Eachmass 280 a, 280 b, 280 c is mounted in a chamber 256 on a shaft 224 soas to be freely rotatable thereabout. Collars 290 a, 290 b are mountedbetween each pair of masses 280 a, 280 b and 280 b, 280 c as shown. Thecollars 290 a, 290 b are similar to the collar 190 shown in FIG. 6 anddescribed above and operate in the same way. However, it is to be notedthat the side of each collar 290 a, 290 b from which two diametricallyopposed pins project is arranged so as to face the central mass 280 b.This ensures that the other masses 280 a, 280 c are prevented fromleading the central mass 280 b or from lagging the central mass 280 b bymore than 180°. In order to ensure that the viscous coupling between theouter wall 254 of the chamber 256 and the central mass 280 b is higherthan the viscous coupling between the outer wall 254 of the chamber 256and the outer masses 280 a, 280 c, fins 281 are provided on the outeredge of the mass 280 b. The distal edges of the fins 281 lie very closeto the outer wall 254 of the chamber 256 and provide high viscouscoupling for the central mass 280 b.

Each of the embodiments described above makes use of a plurality ofcounterbalancing masses which are identical to one another. By this wemean that the masses are identical in shape and are made from materialof the same density so that the centres of gravity of each mass lie atthe same point. Different arrangements for ensuring that the first(leading) mass has a different viscous coupling with the wall of thechamber from that of the or each other mass have been described above.However, it is possible to arrange for the first mass always to lead theor each other mass in different ways. One such way is to provide thefirst mass with a lower moment of inertia than the or each other mass.This can be achieved by ensuring that the centre of gravity of the firstcounterbalancing mass lies closer to the axis of the chamber than thecentre of gravity of the or each other mass. One way to achieve this isto arrange for the mass of the first counterbalancing mass to be lowerthan that of the or each other counterbalancing mass. This is possibleby manufacturing the first counterbalancing mass (or a part thereof)from a material having a lower density than that of the othercounterbalancing mass or masses; by providing the mass portion 382 a ofthe first counterbalancing mass 380 a with one or more hollow cavities383 a (see FIG. 10 a); or by providing the first counterbalancing mass480 a with a number of mass-reducing through-holes 481 a (see FIG. 10b). Alternatively, the mass portion 582 a of the first counterbalancingmass 580 a can be shaped and configured so that, with respect to the oreach other counterbalancing mass, the centre of gravity lies closer tothe axis 518 than that of any other counterbalancing mass used in thesame system (see FIG. 10 c in which the shape of the mass portion 582 bof another counterbalancing mass is shown in dotted outline). In thisarrangement, it is envisaged that the mass of each counterbalancing massis the same as that of the other counterbalancing masses.

Thus it can be seen that the first counterbalancing mass can be arrangedto lead the or each remaining counterbalancing mass by providing it witheither a higher viscous coupling with the chamber wall or a lower momentof inertia than that of the or each remaining counterbalancing mass.Other means for arranging for the first counterbalancing mass to leadthe or each remaining counterbalancing mass will be apparent to askilled reader.

The skilled reader will also appreciate that it is possible to relysolely on the means for arranging for the first counterbalancing mass tolead the or each remaining counterbalancing mass and to dispense withany further constraining means which will physically prevent the firstcounterbalancing mass from lagging the or any other counterbalancingmass. Referring to the embodiment shown in FIGS. 1 to 4, the abutment ofthe pin 92 a against the abutment surface 90 a prevents the firstcounterbalancing mass 80 a from lagging the second counterbalancing mass80 b. However, it is possible to rely on the higher viscous couplingbetween the first counterbalancing mass 80 a and the chamber wall 54 toensure that the first counterbalancing mass 80 a leads the secondcounterbalancing mass 80 b and so the abutment surface 90 a can bedispensed with. A similar change could be made to the embodimentsillustrated in FIGS. 5 to 10.

The scope of the invention is not limited to the embodiments describedabove. It will be appreciated that the shape of the counterbalancingmasses can be varied almost indefinitely as long as the essentialcounterbalancing function is achieved. Indeed, the counterbalancingmasses provided in a single automatic balancing device as describedabove may be different in shape from one another and do not have to beidentical. Different numbers of masses may be provided and alternativemeans for constraining the relative position of the masses may beprovided. A further alternative arrangement contemplated within thescope of the invention is the use of the rear wall of the drum to formpart of the outer wall of the chamber of the automatic balancing device.Other variations will be apparent to a skilled reader.

1. An automatic balancing device for counterbalancing an out-of-balancemass present in a rotating body, comprising: a chamber having an outerwall and an axis, and which rotates with the rotating body, first andsecond counterbalancing masses spaced along the axis and constrained tomove freely in a circular path about the axis and within the chambersuch that, when the device is in use, the first counterbalancing massleads the second counterbalancing mass, a viscous fluid provided in thechamber so as to provide viscous coupling between the outer wall of thechamber and each of the counterbalancing masses when the device is inuse, and a constraint operating at all speeds of rotation when thedevice is in use to prevent the first counterbalancing mass from leadingthe second counterbalancing mass by more than substantially 180° at allspeeds of rotation when the device is in use, wherein the firstcounterbalancing mass and the second counterbalancing mass are spacedalong the axis such that the first counterbalancing mass is spacedfurther from a side of the chamber than the second counterbalancing masssuch that the viscous coupling between the first counterbalancing massand the outer wall of the chamber is higher than the viscous couplingbetween the second counterbalancing mass and the outer wall of thechamber.
 2. An automatic balancing device as claimed in claim 1, whereinthe constraint is adapted to ensure that the angle by which the secondcounterbalancing mass lags the first counterbalancing mass is alwaysless than substantially 180°.
 3. An automatic balancing device asclaimed in claim 1, wherein the constraint further prevents the firstcounterbalancing mass from lagging behind the second counterbalancingmass.
 4. An automatic balancing device as claimed in claim 3, whereinthe constraint is adapted to ensure that the first counterbalancing massalways leads the second counterbalancing mass.
 5. An automatic balancingdevice as claimed in claim 3, further comprising a collar disposed aboutthe axis between the first counterbalancing mass and the secondcounterbalancing mass, the collar being rotatable freely about the axis,wherein the constraint comprises first and second projections extendingoutwardly from the collar so as to engage with shapings of the first andsecond counterbalancing masses and thereby prevent the firstcounterbalancing mass from lagging behind the second counterbalancingmass.
 6. An automatic balancing device as claimed in claim 1, whereinthe first counterbalancing mass has a moment of inertia which is lowerthan that of the second counterbalancing mass.
 7. An automatic balancingdevice as claimed in claim 6, wherein the centre of mass of the firstcounterbalancing mass lies closer to the axis than the centre of mass ofthe second counterbalancing mass.
 8. An automatic balancing device asclaimed in claim 1, wherein the configuration of the first and secondcounterbalancing masses is adapted to cause the viscous coupling betweenthe first counterbalancing mass and the outer wall of the chamber to behigher than the viscous coupling between the second counterbalancingmass and the outer wall of the chamber.
 9. An automatic balancing deviceas claimed in claim 8, wherein, in use, the viscous fluid is in contactwith a larger surface area of the first counterbalancing mass than thesecond counterbalancing mass.
 10. An automatic balancing device asclaimed in claim 8, wherein the surface of the first counterbalancingmass has a shaped or textured portion which faces the outer wall of thechamber.
 11. An automatic balancing device as claimed in claim 8,wherein the first counterbalancing mass is located closer to the outerwall of the chamber than the second counterbalancing mass.
 12. Anautomatic balancing device as claimed in claim 1, wherein the first andsecond counterbalancing masses are supported in the chamber on an axleextending concentrically with the axis.
 13. An automatic balancingdevice as claimed in claim 1, wherein the constraint comprisesstructures provided on the first and second counterbalancing masses. 14.An automatic balancing device as claimed in claim 13, wherein at leastone of the structures of the constraint comprises at least oneprojection extending from the surface of one of the counterbalancingmasses towards the other counterbalancing mass so as to engage with atleast one abutment surface of the other counterbalancing mass.
 15. Anautomatic balancing device as claimed in claim 14, wherein the othercounterbalancing mass has a first abutment surface located and arrangedsuch that, when a projection engages therewith, the firstcounterbalancing mass is prevented from leading the secondcounterbalancing mass by more than substantially 180°.
 16. An automaticbalancing device as claimed in claim 15, wherein the othercounterbalancing mass has a second abutment surface located and arrangedsuch that, when a projection engages therewith, the firstcounterbalancing mass is prevented from lagging behind the secondcounterbalancing mass.
 17. An automatic balancing device as claimed inclaim 15, wherein the abutment surfaces are located on the firstcounterbalancing mass and the projection is located on the secondcounterbalancing mass.
 18. An automatic balancing device as claimed inclaim 1, further comprising a collar disposed about the axis between thefirst counterbalancing mass and the second counterbalancing mass, thecollar being rotatable freely about the axis, wherein the constraint isprovided on the collar.
 19. An automatic balancing device as claimed inclaim 18, wherein the constraint comprises first and second projectionsextending outwardly from the collar so as to engage with shapings of thefirst and second counterbalancing masses and thereby prevent the firstcounterbalancing mass from leading the second counterbalancing mass bymore than substantially 180°.
 20. An automatic balancing device asclaimed in claim 1, further comprising at least one furthercounterbalancing mass provided in the chamber, the arrangement beingsuch that, in use, the first counterbalancing mass leads the furthercounterbalancing mass and the constraint is adapted to prevent the firstcounterbalancing mass from leading the or any further counterbalancingmass by more than substantially 180° when the device is in use.
 21. Anautomatic balancing device as claimed in claim 20, wherein the moment ofinertia of the further counterbalancing mass is higher than the momentof inertia of the first counterbalancing mass.
 22. An automaticbalancing device as claimed in claim 20, wherein the constraint isadapted to prevent the first counterbalancing mass from lagging behindthe further counterbalancing mass.
 23. An automatic balancing device asclaimed in claim 20, further comprising one further counterbalancingmass provided in the chamber.
 24. A washing machine comprising; a drumrotatable about an axis; and an automatic balancing device comprising: achamber having an outer wall and the axis, and which rotates with thedrum, first and second counterbalancing masses spaced along the axis andconstrained to move freely in a circular path about the axis and withinthe chamber such that, when the device is in use, the firstcounterbalancing mass leads the second counterbalancing mass, a viscousfluid provided in the chamber so as to provide viscous coupling betweenthe outer wall of the chamber and each of the counterbalancing masseswhen the device is in use, and a constraint operating at all speeds ofrotation when the device is in use to prevent the first counterbalancingmass from leading the second counterbalancing mass by more thansubstantially 180° at all speeds of rotation when the device is in use,wherein the first counterbalancing mass and the second counterbalancingmass are spaced along the axis such that the first counterbalancing massis spaced further from a side of the chamber than the secondcounterbalancing mass such that the viscous coupling between the firstcounterbalancing mass and the outer wall of the chamber is higher thanthe viscous coupling between the second counterbalancing mass and theouter wall of the chamber, and the chamber and the drum are arranged sothat their axes are collinear.